Klein E E, Harms W B, Low D A, Willcut V, Purdy J A
Mallinckrodt Institute of Radiology, Radiation Oncology Center, Washington University School of Medicine, St. Louis, MO 63110, USA.
Int J Radiat Oncol Biol Phys. 1995 Dec 1;33(5):1195-208. doi: 10.1016/0360-3016(95)00198-0.
Clinical implementation of multileaf collimation (MLC) includes commissioning (including leaf calibration), dosimetric measurements (penumbra, transmission, calculation parameters), shaping methods, networking for file transfer, verification simulation, and development of a quality assurance (QA) program. Differences of MLC and alloy shaping in terms of penumbra and stair-step effects must be analyzed.
Leaf positions are calibrated to light field. The resultant decrement line, penumbras, leaf transmission data, and isodoses in various planes were measured with film. Penumbra was measured for straight edges and corners, in various media. Ion chambers were used to measure effects of MLC on output, scatter, and depth dose. We maintain midleaf intersection criteria. MLC fields are set 7 mm beyond planning target volumes. After shaping by vendor software or by our three-dimensional planning system, files are transferred to the MLC workstation by means of sharing software, interface cards, and cabling. A MLC emulator was constructed for simulation. Our QA program includes file checks, monthly checks (leaf position accuracy and interlock tests), and annual review.
We found the MLC leaf position (light field) corresponds to decrement lines ranging from 50 to 59%. Transmission through MLC (1.5-2.5%) is less than alloy (3.5%). Multileaf penumbra is slightly wider than for alloy. Relative penumbra did not increase in the lung, and composite field dosimetry exhibited negligible differences compared with alloy. Verification simulations provide diagnostic image quality hard copies of the MLC fields. Monitor unit parameters used for alloy held for MLC.
Clinical implementation for MLC as a block replacement was conducted on a site-by-site basis. Time studies indicate significant (25%) in-room time reductions. Through imaging and dosimetric analysis, the accuracy of field delivery has increased with MLC. The most significant impact of MLC is the ability to increase the number of daily treatment fields, thereby reducing normal tissue dosing, which is vital for dose escalation.
多叶准直器（MLC）的临床应用包括调试（包括叶片校准）、剂量测量（半值层、透射率、计算参数）、成形方法、文件传输网络、验证模拟以及质量保证（QA）程序的制定。必须分析MLC与合金成形在半值层和阶梯效应方面的差异。
将叶片位置校准至光野。用胶片测量所得的衰减线、半值层、叶片透射数据以及不同平面的等剂量线。在不同介质中测量直边和拐角处的半值层。使用电离室测量MLC对输出剂量、散射剂量和深度剂量的影响。我们维持叶片中心相交标准。MLC射野设置在计划靶区外7毫米处。通过供应商软件或我们的三维计划系统进行成形后，文件通过共享软件、接口卡和电缆传输至MLC工作站。构建了一个MLC模拟器用于模拟。我们的QA程序包括文件检查每月检查（叶片位置准确性和联锁测试）以及年度审查。
我们发现MLC叶片位置（光野）对应于50%至59%的衰减线。通过MLC的透射率（1.5% - 2.5%）低于合金（3.5%）。多叶半值层比合金的略宽。在肺部，相对半值层没有增加，与合金相比，复合射野剂量测定显示出可忽略不计的差异。验证模拟提供了MLC射野的诊断图像质量硬拷贝。用于合金的监测单位参数适用于MLC。
作为挡块替代物的MLC临床应用是在逐个站点的基础上进行的。时间研究表明室内时间显著减少（25%）。通过成像和剂量分析，使用MLC时射野投送的准确性有所提高。MLC最显著的影响是能够增加每日治疗射野的数量，从而减少正常组织的受量，这对于剂量递增至关重要。
